Several types of passenger conveyor systems, such as, escalators, moving walkways, moving sidewalks, etc. are widely used these days to effectively transport pedestrian traffic or other objects from one location to another. Areas of usage of these passenger conveyor systems often include airports, hotels, shopping malls, museums, railway stations and other public buildings. Such passenger conveyor systems typically have two landings (e.g., a top landing and a bottom landing in case of an escalator) and a a plurality of steps/treads traveling in a closed loop in between the landings. The closed loop forms a load track and a return track interconnected by first and second turnaround sections located at the landings. Passenger conveyors may also include moving handrails traveling together with the steps/treads and a truss structure supporting the treads/steps and moving handrails. The steps/treads may be driven by a step chain (also called an escalator chain) in a closed loop to transport the pedestrian traffic between the two landings. Typically, the step chain is driven by a step chain sprocket and travels in a closed loop forming a load track and a return track interconnected by first and second turnaround sections. In particular configurations of a passenger conveyor system a drive module having a motor and a main shaft drives one or more main drive chain sprockets. The main drive chain sprockets drive the step chain sprocket which is engaged by the step chain. The step chain engages the treads/steps for moving the treads/steps around their closed loop.
The interaction of the step chain with the step chain sprocket often produces fluctuations and vibrations. By way of background, a step chain, like any other chain drive, includes a plurality of discrete chain links, called step chain links, connected together by way of connecting links, such as a pin and a link plate or a roller. A drive sprocket (e.g., the step chain sprocket) includes a profiled wheel having a plurality of engaging teeth for meshing and engaging the connecting links (or possibly even engaging the step chain links) of the step chain, in order to move the step chain as the step chain sprocket rotates. The engagement of the connecting links of the step chain with the engaging teeth of the step chain sprocket causes the step chain to vibrate and fluctuate. These vibrations and fluctuations are often called a polygon effect or a chordal action and not only affect the ride experience of a user (who typically feels these vibrations and fluctuations aboard the passenger conveyor system), but also cause undesirable friction between the step chain and the step chain sprocket, thereby reducing the service life time of those components. Noise generated by the vibrations resulting from the engagement of the step chain with the step chain sprocket is another concern.
Therefore, mitigating or compensating the polygon effect is desirable. Several solutions to reduce or otherwise mitigate the polygon effect have been proposed in the past. Generally, the intensity of polygon effect depends on the velocity of the step chain and the length of the chain links in relation to the diameter of the sprocket. The greater said relation, i.e. the larger the length of the chain links and/or the smaller the diameter of the sprocket, and the higher the velocity of the step chain, the stronger the polygon effect. One possibility for reducing the polygon effect thus is to reduce the pitch of the step chain. In consequence, one approach of mitigating the polygon effect involves increasing the number of step chain links in the step chain (which can reduce the step chain pitch), and/or correspondingly increasing the diameter of the step chain sprocket(s) to increase the number of teeth in engagement with the sprocket (which may also effectively reduce the step chain pitch). This techniques, although effective in improving the riding experience of a user, nonetheless have several disadvantages.
For example, due to the increase in the number of the parts (e.g., increase in the number of step chain links and other associated parts, such as rollers, pins, bushings, link plates, etc., of the step chain, and/or a bigger sprocket), the overall cost of the associated system increases.
Furthermore, the efforts involved with the necessary maintenance of the increased number of components increases, and so does the amount of lubricant needed to reduce the increased wear and tear amongst those components. This increased wear and tear can additionally reduce the service life time of the step chain and the step chain sprocket. Moreover, the aforementioned approach does not address to the noise issue discussed above, and may in fact increase the noise due to a greater engagement of the step chain with the step chain sprocket.
WO 2012/161691 A1 discloses a polygon compensation coupling system for reducing a polygon effect in a chain driven system, the polygon compensation coupling system including a chain sprocket and a main drive in engagement with the chain sprocket, such that the engagement defines a compensation curve to reduce the polygon effect.
U.S. Pat. No. 6,351,096 B1 and WO 01/42122 A1 disclose an electronic drive system, which is configured to control a motor driving the sprocket of a chain drive so that it rotates with non constant velocity, the non-constant rotation of the sprocket compensating the polygon effect.
WO 03/066501 A1 describes to a pulse free escalator system having two spaced apart pulse free turnaround sections. The escalator system has a pair of guide tracks and a pair of linkage assemblies, each comprising a plurality of links joined together. Each linkage assembly has a plurality of rollers for supporting the linkage assembly which travel in a respective one of the guide tracks. Each guide track has two spaced apart turnaround portions with each turnaround portion defining a travel path for each roller having first and second constant radius sections adjacent to a linear entry section and a linear exit section, respectively, and a pulse-free section intermediate said first and second constant radius sections.
EP 1 479 640 B1 and U.S. Pat. No. 4,498,890 teach to compensate the polygon effect by providing a curved track section having a varying curvature in the linear portion of the chain next to the sprocket. Such curved track sections, however, reduce the usable length of the chain loop, as the portion of the loop in which the curved section is located may not be used for transportation.
Accordingly, there is a need for a more effective solution to compensate the polygon effect in chain drives. It would be particularly beneficial if such solution provided a convenient tool to provide sufficient polygon compensation for chain drives of any geometry.
In addition it would be particularly beneficial to have available a polygon compensation technique that improves the riding experience of the users without incurring any additional costs associated with increasing the step chain links or with using a larger diameter step chain sprocket. It would further be beneficial if such a technique were reliable, easy to maintain, increased (or at least did not negatively impact) the service life time of the step chain and the step chain sprocket (e.g., by reducing wear and tear), and additionally provided a greener approach (by using less lubricant) to solving the polygon effect problem. It would additionally be desirable if this technique reduced the noise generated by the step chain and the step chain sprocket engagement and would not reduce the usable length of the chain.
Although the embodiments described herein focus towards a step chain driven passenger conveyor system, it be understood that similar problems with respect to occurrence of a polygon effect apply to other chain driven systems as well, and therefore the solutions suggested below may be beneficial to other types of chain driven systems, in particular to other types of chain driven conveyor systems.